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THE SOUNCl ENGINEERING MAGAZINE
AUGUST 1973 $1.00
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(A California Corporation)
Circle 10 on Reader Service Card
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COMING
NEXT
MONTH
• Studio Rumbles by Michael Ret-
tinger is an examination by this noted
acoustical consultant on the problems
of low frequency rumble in the studio.
Cures are offered.
Sidney L. Silver takes a look at the
PSYCHOACOUSTICAL ASPECTS OF SoUND.
The insight to be gained cannot help
but be of considerable value to the
audio engineer.
Part 2 of William Rheinfelder's ar-
ticle concludes what is begun in this
issue with the Musician's Tone Con-
trol.
db Visits — Harvey Radio. Associ-
ate editor John Woram and pictures
of this important New York City dis-
tributor of pro audio and video equip-
ment. Our excuse for going was a
recent open house.
September is AES Convention month
so we will have a map and rundown
of hours and places.
And there will be our usual colum-
nists: Norman H. Crowhurst, Martin
Dickstein, and John Woram. Coming
in db, The Sound Engineering Maga-
zine.
ABOUT
THE COVER
• This ultra modem record player is
a portend of part of what's coming at
the 25th anniversary Convention of
the AES next month. Please do not
send orders for the unit to us since
we are not authorized dealers and
have no stock.
THE SOUND ENGINEERING MAGAZINE
AUGUST 1973 VOLUME 7, NUMBER 8
19
21
27
db VISITS— SOUND 80 STUDIOS
NEW APPROACHES TO TONAL
REPRODUCTION, PART 1
W. A. Rheinfelder
THE LI'L LIMITER
David A. Howe
2 LETTERS
4 THE SYNC TRACK
John Woram
8 THEORY AND PRACTICE
Norman H. Crowhurst
13 SOUND WITH IMAGES
Martin Dickstein
16 PICTURE GALLERY— 45th AES CONVENTION
29 BOOKCASE
30 CLASSIFIED
32 PEOPLE, PLACES. HAPPENINGS
db is listed in Current Contents: Engineering and Technology,
Robert Bach
PUBLISHER
Bob Laurie
ART DIRECTOR
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CIRCULATION MANAGER
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ASST. CIRCULATION MGR.
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EDITOR
John Woram
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COPY EDITOR
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ASSISTANT EDITOR
GRAPHICS Crescent Art Service
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contents copyright © 1973 by Sagamore Publishing Co.. Inc.. 980 Old Country Road. Plainview. L.I.. N.Y.
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<
n
•D-
csi
One of a series of brief discussions
by Electro-Voice ertglrteers
THE
f WELL-BEHAVED
OlAPKftAGM
U P.H H WATSOH
Minronhcnts
When a microphone design engineer finds dis-
departing from ideal piston operation. The big
microphone under test, he can usually assume
that any pealcs and/or dips are the result of
either faulty damping or that the diaphragm is
departing from Ideal piston operation. The big
problem has been to determine which fault Is be-
ing displayed.
A powerful tool in determining actual diaphragm
behavior is the holographic camera. It can reveal
and measure the deformations of the diaphragm
not visible by other means. Use of this research
method led to the unusual diaphragm used In the
new E'V Model DSSS Single-D microphone.
The problem was to design a diaphragm that
offered high compliance at low frequencies yet
maintained good rigidity at high frequencies to
withstand the high accelerative forces without dia-
phragm breal(up. The solution was to combine an
Acoustalloy® diaphragm using a semi-toroidal
surround plus a flat center section, to which Is
bonded a domed "pill" of molded polystyrene.
This construction reduces piston brealtup over a
broad range of frequencies, and eliminates the
minor resonant areas typical of more complex dia-
phragm designs. Mass of the moving system is
alsa controllable within very close tolerances. The
result is predictably flat response, especially at
higher frequencies.
This flat response, in addition to being desir-
able in itself, mattes possible more unform off-
axis performance since adjustments can be made
to the phase-shifting networlts necessary for cre-
ating a cardioid pattern, without upsetting the on-
axis response.
The holograms also revealed a need to mount
the voice coil more rigidly to the diaphragm to
eliminate the decoupling that can talte place at
high frequencies. This was done by recessing the
rear surface of the diaphragm to permit the coil
cement to operate in shear rather than the usual
compression-expansion mode typical of other de-
signs. This improved mounting was made possible
by the unique volumetric nature of the diaphragm
assembly.
The net result of this design program was to
create a single-D microphone that Is remarlcably
uniform in response both on-and off-axis, espe-
cially in the region from 3 to 10 ItHz where non-
linear diaphragm motion is relatively common
with traditional designs. The same approach to
diaphragm construction has also been applied to
other E-V sIngte-D microphones including the 670
series.
Where the microphone is used for sound rein-
forcement a distinct movement can be noted in
gain-before-feedbacl( as a direct result of the
reduction of pealcs in both on- and off-axis modes.
In addition, elimination of pealts reduces the
lllcelihood of input overload in critical installations.
For reprints of other discussions In this series,
or technical data on any E-V product, write:
ELECTRO-VOICE, INC., Dept. 833BD
686 Cecil St., Buchanan, Michigan 49107
Circle 22 on Reader Service Card
letters
The Editor:
After my seventh article in three
years appeared in your pages early
this year I am reminded that I haven't
been able to thank individually all
those readers who have taken the time
to give me some kind of feedback,
through either constructive criticism
or complimentary acknowledgement.
I hereby do so, with sincere thanks
for their remarks.
In an isolated case, the comments
of one W. Dixon Ward, which you saw
fit to publish in an un-rebuttable man-
ner, deserve especial attention. For, his
views on both the subject of hearing
and my treatment of same have done
more to prove one of my key points
than anything I could have said my-
self. Namely: an expert is one who
knows more and more about less and
less.
Marshall King
Hollywood, California
advertisers
index
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Lumiere Productions . . . . 10
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Perception 12
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Quad-Eight 26
Ramko Research 8
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Schoeps 16
Shure Cover 3
Timekeeper 6
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The most important
microphone book ever published.
Covers every significant aspect
of theory and use from A to Z!
LOU BURROUGHS
Microphones:
Special Offer
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This soon-to-be published book is complete, up-to-the-
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Sagamore Publishing Co. (publishers of db The Sound
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Perfect for Reference or Trouble-Shooting
The twenty-six fact-packed chapters in this indispen-
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you meet in day-to-day situations. For example:
• How does dirt in the microphone rob you of response?
• Which mic would you pick for a large auditorium?
• How are omni-directional mics used for orchestral pickup?
• When would you choose a cardtoid, omni-directional or
bi-directional mic?
• How do you space your microphones to bring out the best
in each performer?
Author
Lou Burroughs is widely known for his pioneering work
with Electro-Voice and is one of the universally recog-
nized experts in the field. He helped design and develop
many of the microphones which made modern broad-
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acoustical products! Lou Burroughs knows microphones
inside out. This book is based on his many years of
research, field studies and lectures given throughout
the world.
Exclusive Pre-Publication Offer
lUicrophones: Design and Application will be offered to
the general public at $20.00. But for a limited time, db
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To take advantage of this reduced rate, your order must
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copy at the special pre-publication price.
PRE-PUBLICATION RESERVATION ^
Sagamore Pubfishing Co. Inc. 980 Old Country Rd. Plainview, N.Y. 11803 >
Please reserve ( ) copies of MICROPHONES: DESIGN AND APPLICATION at $13.50 eacti postpaid. Rusti shipment upon publication. <§
Name t , , < » "
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OS
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Please Note: THIS PRE-PUBLICATION ORDER FORM IS VALID TO OCTOBER 30, 1973, AFTER WHICH THE PRICE WILL BE $20.00. oj
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THE SYNC TRACK
Circle 17 on Reader Service Card
• Last month's column went on about
keeping the number of microphones
used on a session down to some sort
of sensible minimum. As noted, this
requires more control in the studio.
Groups of instruments are recorded in
stereo, with the balancing chores be-
ing assumed more by the conductor
than the engineer.
But, what about planning during a
mixdown? How does one shift the ap-
parent location of an instrument re-
corded in this manner?
At times, one doesn't. Even a single
instrument recorded on a stereo pair
of tracks cannot be re-located later
without losing the effectiveness of this
particular recording technique.
Consider for example, a solo french
horn overdub. The musician sits in
the middle of the room and is picked
up by two microphones — each feed-
ing a separate track. Later, the tracks
are located left and right, so that the
horn appears to be located in the cen-
ter. But now, although everyone likes
the stereo sound, the producer asks
you to locate the horn on the extreme
right. How can this be done? Of
course, you can remove the track feed-
ing the left speaker, or pan it over
to the right along with the other track.
Either way, the horn comes up on the
right, but the stereo effect is lost.
In order to maintain a stereo effect,
the horn would have to be recorded
all over again, with the musician actu-
ally sitting off to the right. In stereo
miking, directional information is a
function of many variables; musician-
to-microphone distance, space between
microphones, angle of microphones,
etc. The actual sound pressure level
at each microphone might be about
the same and yet the instrument would
definitely appear to be located on
the right.
This is quite different from pan-
ning a single track to produce the
desired localization, because when a
single track is panned to the extreme
right, nothing comes out of the left
speaker. In stereo miking, the left
speaker is still active, as just noted.
So, why even bother with stereo
miking when using a single track ap-
pears a lot simpler, and lets you easily
relocate the instrument during mix-
down? Obviously, you can't go back
and re-record an instrument every time
you wish to try a new location.
In a situation like this, the engineer
must carefully consider the advantages
of both techniques. Once again, a
good understanding of the technology
will help.
www.americanradiGhistorv.com
When a single track is to be located
at a specific point between left and
right, it is panned so that the propor-
tion of left-versus-right signal gives
the listener the desired impression.
However, we are assuming the listener
is located midway between the speak-
ers. But, if the listener is sitting to
the left of center, while the signal is
panned to the right of center, the net
effect may be that the signal appears
to be coming from dead center. In
other words, as the listener moves
around, so does the apparent location
of the sound source. If the signal is
panned completely to one side, the
sound may not shift as the listener
moves, yet those sitting near the op-
posite side will hear a considerably
unbalanced program.
With stereo miking, listener posi-
tion is less critical. Although localiza-
tion information may be a little more
subtle, there will be less apparent shift-
ing as the listener moves about. And,
the instrument or instruments recorded
in stereo will sound as though they
are occupying space in a room, rather
than as though they were point sour-
ces of sound.
Of course, the engineer must know
where the instrument's sound is to
come from before making the record-
ing. In the case of an overdub, the
eventual location of which is unde-
cided at the time of recording, there
may be no point to a stereo pickup.
If it is known that the overdub will
be on either the left or the right, then
it might be recorded as a left-originat-
ing sound, and the tracks reversed
later on to relocate on the right. How-
ever, shifts from either corner to the
center, or vice-versa, could not be
made.
On a multi-track tape with sixteen
or more sources of sound, the sonic
subtleties of a stereo overdub may be
minimal at best. Yet, if the overdub
is the featured soloist, as is usually the
case on a pop session, stereo miking
may be well worth considering.
Under this condition^ it is usually
certain that the soloist will be located
in the center. If the orchestral back-
ground has been carefully recorded
and mixed to present a wide program
source, it may be difficult to blend in
the soloist in the right proportion. At
one extreme, the soloist may be buried
in the accompaniment and at the
other he (or she) will stick out like
a sore thumb. On some recordings, it
is all too obvious that the featured
singer was added long after the band
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Of course, stereo miking will not
eliminate all the problems of the lay-
ered performance. But, if the singer
is recorded in stereo, it wil be a lot
easier to get a better vocal-orchestral
blend. The stereo effect will create a
feeling of some spaciousness, so that
the singer will seem to be singing in
a room rather than in a closet. Now,
when the orchestra tracks are brought
up, the vocal track(s) will fit more
naturally.
Stereo miking does require some
care, especially on vocal pickups. The
distance between the microphones
should be noted, and no one placed
closer to the microphones than three
times this distance to avoid cancella-
tion effects.
Therefore, at the tight working dis-
tances preferred by many singers, the
mics will have to be extremely close
to each other. The charm of an "inti-
mate" sound notwithstanding, the
stereo effect will be minimal, or non-
existant at super close range, so you
may as well dispense with the stereo
pickup in this case. However, if the
orchestra is of any appreciable size,
the vocal may sound a lot better with
a Uttle distance between tonsils and
mic diaphragm. ■
Copies of db
on Microfilm
Copies of all issues of db — The
Sound Engineering Magazine start-
ing w/ith the November 1967 issue
are now available on 35 mm. micro-
film. For further Information or to
place your order please w/rite di-
rectly to:
University Microfilm, Inc.
300 North Zeeb Road
Ann Arbor, Michigan 48106
A subsidiary of Xerox
Corporation
In addition to Microfilm Copies
available through University l^icro-
film. we have a limited number of
regular back issues available. You
may order these copies at $1.00
each from:
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db — The Sound Engineering
Magazine
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THEORY AND PRACTICE
• Waveform analysis and synthesis
is one of those theory-wrapped sub-
jects that comes up from time to time,
and has" its quota of misconceptions.
In the field of audio, because fre-
quency content has been proven to be
more important than phase relation-
ships between the frequencies present,
efforts to correlate content and wave-
forms have not been too frequent.
They occur more frequently in other
electronic applications.
But there is an important difference
in ways that signals can be generated,
that relates to the basic reference quan-
tity used — frequency or time — and has
also intruded much more upon the
audio scene since the advent of syn-
thesizers, and of function generators
in particular.
In the old days, BFG (before func-
tion generators), all signal generators
used one or other kind of oscillator
in which various components of the
circuit determined frequency, much
like the pitch of a musical instrument
is determined. In the case of a stringed
instrument, the pitch is determined
by the mass and length of the vibrat-
ing portion of the string, in conjunc-
tion with its tension.
In the old L-C oscillator circuit,
this was almost a direct counterpart
with the L and C of the tank circuit.
The correspondency was a little less
obvious in oscillators of the feedback
or phase-shift variety, but the fre-
quency of oscillation was still basically
determined by various circuit compon-
ents, as definitely as it depended on
the L and C of its predecessor.
In those days there was another
kind of oscillator, known as a "relaxa-
tion oscillator," of which the multi-
vibrator was one. It was best known
for producing a square wave, although
with variations it also produced the
sawtooth, which came into demand
with the advent of the oscilloscope
and, later, television.
This was really the beginning of
waveform generators that were not
frequency based, but time referenced.
Intervals in the "action" were deter-
mined by circuit time constants, where
all the earUer circuits, both L-C and
phase shift, were dependent on the
reactance of circuit components at
specified frequencies.
In the L-C circuit, of whatever type,
frequency was fixed where the reac-
tance of L and C had identical value
in the tank circuit, but opposite sign,
of course. In a phase shift oscillator,
usually three capacitors, in conjunction
with resistors, each produced a phase
shift, the total of which added up to
180 degrees at the operating frequency,
which was thus fixed by the combina-
tion of three sets of R and C values.
In the feedback oscillator, usually
two R's and C's were combined so that
the net work produced zero phase shift
at a particular frequency where their
reactances and resistances produced
the necessary symmetry. In another
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variant, the network was a twin-T,
with three R's and three C's in a net-
work that either produced a null at
the operating frequency, or else pro-
duced precise phase reversal (180
degrees) at that frequency.
In all those circuits, frequency was
determined by the reactance of com-
ponents in the circuit.
In the relaxation oscillator, an ac-
tive device such as a tube — now re-
placed, usually far more effectively,
by a transistor — alternated between
two conditions, conducting and non-
conducting. What controlled this
change was the voltage in a resistor-
capacitor combination. With the ca-
pacitor fully charged in one direction
by the action of the circuit, the active
device had its action suspended, until
the voltage on the capacitor leaked
away through the resistor, according
to the circuit time constant, to a
critical point.
At that point, the active device
would trigger the next action of the
circuit. This kind of circuit is time
referenced. Where it generates a square
wave, the length of the flat top and
bottom of the square wave is deter-
mined by the time constants of the
R and C components, and by certain
voltage ratios set by the design of
the circuit. Such a circuit can have its
frequency controlled — really by con-
trolling the period duration — ^by ap-
plying a variable voltage to that part
of the circuit where the R-C time
constant sets the interval.
A frequency referenced square wave
could be made — and some early cir-
cuits generated them this way — by
starting with a sine wave oscillator,
which was the basic shape generated
by all frequency referenced oscillators,
even if it was often not a very good
sine wave, and then clipping its tops
and bottoms off.
The first such clipping would make
a trapezoidal wave, one with horizon-
tal top and bottom, but sloping sides,
because the sides of a sine wave slope.
By amplifying and clipping again, the
sides could be steepened as much as
you want. It was never a perfect
square wave — ^but then, if you want to
be particular, a perfect square wave
has never been generated. Its fre-
quency, of course, was always that of
the sine wave from which it started.
The relaxation oscillator almost in-
evitably had steeper sides than this
fabricated, wave-shaped variety. The
circuit produced a trigger action which
very rapidly flipped the circuit from
one bistable condition to the other.
Usually one of a pair of active devices
is always non-conducting, while the
other is conducting. Come trigger time,
both of them amplify for a split sec-
ond, and the situation is reversed.
TRIGGER POINT
Fig. 1 How a triangular wave is built.
The function generator, in a way,
provides the link that brings us back
to where we started. Wc were able to
generate cither a sine wave, with a
machine that is frequency referenced,
or a square wave (or other shape)
with a machine that is time referenced,
and we could convert a sine wave into
a square wave. Now the function gen-
erator gives us a means of making
a sine wave that is time referenced.
The basic function used in such a
generator is similar to that described
for the relaxation oscillator, but the
function generator does it with more
precision. Instead of a simple R-C
charge circuit, the function generator
has a constant current circuit that can
alternately charge a capacitor in oppo-
site directions.
During each such charging action,
the voltage on the capacitor is a linear
slope, producing one of the slopes of
a triangular wave (Figure 1). This
charge goes on till the voltage reaches
a preset trigger point in that direction,
when the charge direction is reversed,
and the slope goes the other way.
When the voltage gets to the other
trigger point, then it is turned back
on its first slope course.
The shape of such a wave is deter-
mined by the voltage distance between
the trigger points, and the slopes of
the lines going back and forth between
them — again, this is a time referenced
operation.
Having generated a perfectly con-
trolled triangular wave, it can now
be shaped into virtually any symmetri-
cal waveform. Shaping it into a near
perfect sine wave is a cinch. Using
diodes appropriately biased to change
Fig, 2. Two-frequency synthesis of a
single-ended pulse
RESULTANT
FUNDAMENTAL
2 ND
the slope at successive intervals of
voltage change, a sine wave with low
fractional percent distortion is easily
and consistently produced.
Such a circuit can have tremendous
advantages m producing very low fre-
quency sine waves, of equally perfect
form, that would be impossible with
any of the older type circuits. If you
want a sine wave that completes its
cycle once every ten minutes, no prob-
lem!
As readers are undoubtedly aware,
music synthesizers use generators ca-
pable of producing any of these wave-
forms, using voltage control for both
frequency and amplitude. Actually, to
be academically correct, such gener-
ators do not control frequency; they
control periodicity. Where the old fre-
quency referenced oscillators worked
because certain reactances took effect
at so many hertz (usually called cps
in those days) the new ones set the
individual period length in micro-
seconds.
Academic, admittedly, but it helps
understand the differences in how they
work. There is another difference. A
frequency referenced oscillator has to
"get going." If it produces a good
sinusoidal waveform, it usually takes
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A recording engineer
relies uDon his eors
Whoi is heard at Ihe
console deermines
he fino'mix
For successful quadraphonic
mixdown, a properly controlled
acoustical environment is even more
important than for two-channel
stereo. Psycho-acoustic effects must
be considered in relation to estab-
lished principles of acoustics when
laying out a quadraphonic monitor-
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A professional consultant expe-
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Best of ^11, if called in the planning
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Circle 31 on Reader Service Card
FOR COMPARISON
Fig. 3. Synthesis of the same pulse,
using 6 frequencies. The successive
series are:
t
t + i/4.2t
f + 2/5-2t+ 1/15-3f
f + 1/2-2f + 1/7-3f + 1/56-4f
f + 4/7-2f + 3/14-3f + 1/21-4f +
1/210-5f
f + 5/8-2f + 5/18-3f +-1/12-4f +
1/66-5f+ 1/792-6f
a good many cycles of any particular
frequency to reach a stable level. The
function generator, on the other hand,
produces its first cycle perfectly, at the
same level as all subsequent cycles, un-
less the voltage operated amplitude
control is used deliberately to change
amplitude.
There are other differences between
frequency and time referenced cir-
cuitry and operation. And this was
what started me off at the beginning,
although I have digressed by showing
the practical significance first, in the
way different generators operate. This
distinction can be demonstrated by
considering pulses from two view-
points: frequency synthesis and time
analysis.
Frequency synthesis would use either
a Fourier series — which must be taken
to infinity before you see the result —
or a successive finite series, to ap-
proach the ultimate,, ideal waveform.
Time analysis considers only its shape
through time — how the voltage rises
and falls within the duration of the
pulse.
Using the successive finite series, a
fundamental with 1/4 amplitude sec-
ond harmonic makes a first approxi-
mation to a pulse (Figure 2). If you
add some third of 1/15 amplitude,
you can raise second to 2/5. As you
add successive harmonics, you can
raise the value of earlier ones, slowly
getting something that looks more like
a pulse. Figure 3 shows the form
produced with harmonics up to sixth.
For comparison, we show a pulse
produced by drawing one cycle, from
bottom peak to bottom peak, of just
the 6th harmonic. That is more like
what a pulse generating circuit that is
time controlled would produce, if it
had a switching time equal to half a
period of the 6th harmonic.
The reason for the radical difference
is that the frequency synthesis route
is analogous to a balancing act. All
those diminishing magnitudes of har-
monics are devoted to ensuring that
no ripples occur in the interval be-
tween pulses. The sharpness of the
pulse is limited by the larger magni-
tude, fundamental and lower harmon-
ics, combining, and thus is much
broader than just a cycle of the 6th
by itself.
Space has just about run out on me
for this time. I had wanted to com-
pare the Fourier analysis of various
waves of straight line form with that
produced by successive finite series
approach. This is quite instructive,
but will have to wait for another time.
As you may probably know, wherever
you cut off the Fourier synthesis, you
are left with a wave that has ripples
on it. And since you cannot get fre-
quencies up to infinity, even with mod-
em technology, how can one have the
good-looking square waves, sawteeth
(sawtooths?) that we have seen dis-
played on CR tubes? The successive
finite approach shows how, as well as
helping to understand the difference
between synthesis and analysis, as be-
ing not merely the inverse of one an-
other. ■
you write it
Many readers do not realize that they
can also be writers for db. We are al-
ways seeking good, meaningful articles
of any length. The subject matter can
cover almost anything of interest and
value to audio professionals.
Are you doing something original
or unusual in your work? Your fellow
audio pros might want to know about
it. (It's easy to tell your story in db.)
You don't have to be an experi-
enced writer to be published. But you
do need the ability to express your
idea fully, with adequate detail and
information. Our editors will polish
the story for you. We suggest you first
subniii an outline so that we can work
with you in the development of the
artio.'e.
You also don't have to be an artist,
we'll re-do all drawings. This means
we do need sufficient detail in your
rough drawing or schematic so that
our artists will understand what you
want.
It can be prestigious to be published
and it can be profitable too. All arti-
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www.americanradiohistorv.com
Martin Dickstein
SOUND WITH IMAGES
Projector
Care and Maintenance
• Last time, several ideas concerning
the care-taking of tape recorders, both
audio and video, were discussed. Cer-
tainly, there are many more tricks
and techniques that are known by
those who work with these devices in
all circumstances of operation, such
as the type of cleaning liquid most
satisfactory, head demagnetization sug-
gestions, and so on. Similarly, there
are some simple ways to keep projec-
tors working satisfactorily with a
minimum of down-time.
Film projectors have a few more
moving parts accessible to the oper-
ator than does a tape recorder; each
of these parts should be checked very
often to make sure they are clean and
in good shape to protect the film and
to offer a smooth and clean presenta-
tion. In most industrial audio/visual
installations, the most-used projectors
are those for 16mm film and 35mm
slides. Others in lesser 'use are for
35mm film, slide projectors for differ-
ent size slides, strip projectors, etc.
In general, film projectors are similar
within any one class, and in this dis-
cussion, certain units will come to
mind immediately; others will be able
to be handled in a similar manner
although type, location of parts, and
other dissimilarities may exist.
In the 16mm film class there are
generally two types — the kind that will
thread automatically and the type that
requires manual threading. The film
path is the same in both — past a series
of rollers, around motor driven gears,
around a sound drum, past idlers, and
up to a takeup reel. These all make
sure the film moves smoothly. One
essential segment of the film path was
omitted — the small section where the
film goes through a gate, past an
aperture, in front of a source of
light, and is pulled through by a
toothed mechanism at the proper
speed to provide smooth flow of mo-
tion on the screen. It is this film path
and projection system that we'll dis-
cuss, first.
Starting with the source of light,
the projection lamp is housed in a
protective enclosure to keep the light
output from straying out of the film
illumination path and into the room,
projections booth or the eyes of the
projectionist. (This housing gets quite
hot and care should be taken when
working around the area during use.)
Some of the light does escape through
the top of the projector through the
vented area over the housing. This
opening is actually provided for the
escape of the heat from the lamp. A
fan in the projector operates normally
as long as the motor power is sup-
plied. This means, therefore, that as
soon as the projector is stopped, the
fan also goes off. In a great many pre-
sentations, the film showing is done
in start/stop fashion, and this process
can go on for some time. Heat is not
usually carried away sufficiently dur-
ing actual operation, so that when the
projector motor is off, the heat in and
around the lamp housing escapes only
by the air convection in the room. The
longer the start/stop process, the great-
er the heat accumulation. The housing
and any controls in the immediate
vicinity of the lamp remain hot and
can possibly cause injury.
There are, therefore, several obvious
conclusions to be drawn, suggestions
to be made, and some questions. Un-
der all circumstances, care must be
taken while working at or near a pro-
jector during a showing. The projec-
tion room should be well ventilated,
not only for the good of the projector,
but also for the well-being of the pro-
jectionist. For ease (not always speed)
of rewinding the film after a presen-
tation, the projector is turned on. This
provides fan circulation to the lamp
and housing and will prolong the life
of the lamp. For cooling efficiency, it's
obvious that the area through which
the circulating air must move should
be clean and clear of obstruction.
Enough room must be left around the
projector, if the unit is installed in an
enclosed area, to permit the air to
move freely. Nothing should be
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Circle 21 on Reader Service Card
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Circle 18 on Reader Service Card
placed on the projector where the hot
air emerges, and the area in which
the unit is placed should be kept clean
of dust, cigarette ashes, and any dirt
particles which can be drawn up or
into the projector. (In the event the
lamp blows during a showing, extreme
caution must be exercised to avoid
injury during replacement.)
The difficulty and danger of a sud-
den lamp failure, as well as the delay
that causes during the presentation,
can be forestalled by changing the
lamp when it starts to turn dark or
gray and when the slightest sign of
a blister in the glass of the lamp starts
to show up. If precautions are taken
and the lamp replaced before the ex-
pected life of the lamp runs out, down-
time of the projector will be reduced
sufficiently to make the trouble of the
precaution worth while.
To keep the lamp output at speci-
fied level, it also helps to maintain
the rest of the illumination components
in the best operating conditions. The
brightness and sharpness of the image
in presentations are maintained at peak
level when the lenses and heat filter
are kept clean. Depending on the type
of projector, the lenses may or may
not be readily accessible, but in most
cases, with care, they can be taken
out of the projector with only a min-
imum of effort. These lenses should
be checked regularly and cleaned care-
fully with lintless lens paper or lens
cleaner. Finger prints should be re-
moved completely without scratching
the glass before the lenses, either
front or rear, are replaced into proper
position. In most instances, the lenses
are keyed in their individual mounts
and the glass should not be removed
from the frames. The mounts are usu-
ally also keyed so that each unit can
only fit into one place in only one
way. This assures proper replacement
after cleaning.
In some projector units, the heat
filter is not removable but can l-
reached with the lenses removed. This
glass also needs cleaning periodically
with lintless lens paper or cleaner. ( If
the heat filter cracks or breaks, it
should be replaced as soon as pos-
sible. The projector should not be used
without the filter or the film will
bum.) If the lenses crack, this some-
times will not be noticed just by watch-
ing the image, since only a small
amount of light might be lost and not
noticed. If the picture will not come
up at all on the screen, it will be
possible that a broken condenser lens
might be the answer.
The reflector in the lamp system
is located behind the lamp and directs
the light that is thrown toward the
rear of the projector back toward the
film illumination path. This reflector is
usually factory installed and adjusted.
It rarely requires continual attention,
but should be inspected and cleaned
occasionally to assure proper image
brightness. Care should be taken to
avoid damaging or scratching the re-
flector surface. It should be cleaned
with lens cleaner or lens paper, taking
care not to leave fingerprints or lint.
The film path must also be clean.
In the type of projector which has a
lens which only moves forward and
back (usually in the manual-load
type), there is also a removable gate
shoe that can collect lint and dirt
which will show up on the screen.
It not only looks bad but some of this
debris could possibly scratch the film.
Directly behind the shoe is the aper-
ture through which the lamp beam
reaches the film. The rollers,, idlers,
toothed gears and pulldown mechanism
are also part of the film path. All of
these locations, the space around the
aperture, and the sound drum must
also be kept clean with a cleaning
fluid and clean, lintless cloth or brush.
In the model which permits swing-
away lens holder movement, the path
around the aperture can be reached
easily. Otherwise, as in the manual
load projector, it is necessary to insert
a probe such as a pipe cleaner to
cleanse the aperture and path. Cau-
tion must be observed to prevent dam-
age to the lamp and other items in
the path, and especially, no cleaning
should be performed while the ma-
chine is in operation, for the sake
of the projector and the operator.
One other place to look for trouble
before it starts is in the spring action
of the gate shoe or pressure plate de-
pending on the projector. The tiny
springs that provide the pressure on
the film during its motion past the
aperture are held in place by tiny
screws. The screws should be checked
for tightness and the spring for ease
of movement. If one of the springs
gives way, or if one of the screws
loosens or goes through the plate a bit
too far, the film can be badly torn
or scratched — ruined, possibly.
Also in the line of preserving the
life of the film, it would be wise to
clean the film periodically to prevent
dust or oil from collecting on it and
damaging the image. The dust could
also come off in the projector and in-
troduce the possibility of future trou-
ble. There is a film cleaning solution
which is recommended. A piece of
soft velvet can be used to apply it
HIT! I, ni-CL
.1
Presenting The
VARI-BAND SWEEP EQUALIZER!
Equalization any way the ear can hear it.
Continuously variable bandcenter, bandwidth
(slope) and amplitude at a price comparable to
non-sweeping equalizers.
P. 0. Box 31 87, Hollywood, CA 90028
1965 Cheremoya Ave., Hollywood, CA 90068
(213) 467-7890
IS
Circle 16 on Reader Service Card
www.americanradiohistorv.com
during a normal rewind process. One-
and-only or special copies of films
might also be handled with white
gloves, just to make sure they stay
clean and in good shape.
Another thought on handling film —
when attaching the film on the pro-
jector to the take up reel, an adhesive
tape should not be used, especially if
the projector is of the auto-load type.
If, when the tape is rewound, it is
run back through the normal film path,
the adhesive material could possibly
catch in the gear or gate mechanism
and remain to cause trouble on the
next loading. At least with a manual
load unit, if the adhesive sticks some-
where, removal of the film is quicker
and easier than with the auto-load
units. Of course, on either projector,
if the film path at the aperture is
opened up by movement of the lens
and the pressure plate or shoe, the
sticky stuff may not stick at the aper-
ture, but it can foul gears or the
sound drum. (And, speaking of film,
if any film develops broken sprocket
holes or a bad splice where either the
loop is lost or the film parts, the film
should not be used again until the
damage is repaired properly.)
Much of the care that goes into
maintaining a film projector can also
be applied to a slide projector. There's
no path of movement past an aperture,
but there is movement of parts; there
is a lamp/lens heat filter system for
projecting an image onto a screen and
care of these parts is the same as for
a film unit. The same technique is
used to clean these parts with the
same materials as in the movie pro-
jector. Care of slides is similar to that
of film. Ventilation for the lamp is
the same as in the film projector ex-
cept that in some projectors the fan
can be turned on without the lamp,
while in others this is not possible.
Replacement of lamps, lenses, etc.
should be done with the same care as
in the film projector. In some of the
slide projectors, the fan can be left on
after a presentation to cool the lamp.
This can come in handy to change
the lamp during a presentation (if this
does become necessary). It would be
wise to replace the lamp before its life
is completely gone — as in the film pro-
jector. Here again, the same precau-
tions must be taken in positioning the
slide projector. Air must flow cleanly
around and through the unit to help
cool the lamp. Although normal oper-
ation of the fan usually does not keep
the lamp cool enough to handle, it
does keep it from breaking. The air
passing through the projector should
be cool, clean, and the air vents should
be left unblocked. In those units in
which the cooling air is brought into
the projector from the bottom, the pro-
jector should not be placed on a soft
surface (like a chair or sofa) to per-
mit easy flow of air.
You will recall that this whole dis-
cussion of care of equipment started
(in the last column) with a voicing of
opinions by industrial users of such
equipment and the dissatisfaction they
expressed with the lack of helpful hints
passed on by the equipment salesmen
(aside from the equipment manuals
that come with the units). Other ques-
tions that came up were concerned
with whether it mattered if the pro-
jection lamp was handled carefully or
not (prints, etc.), whether the fan on a
slide projector could be left on too
long so that the lamp could possibly
reach a temperature below the room
ambience and then blow if it were
turned on suddenly, whether it was
really necessary to cool the lamp with
the fan at all or if this cooled the
lamp too fast for its own good and
if the lamp were safer with just turn-
ing off the projector. Any ideas by our
readers on these or any other points
would be appreciated. ■
DRT CAN BE HARD
nnNDfSEN
make your communications
"WHISPER-CLEAN"
MS-180
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MAGNETIC
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CONTACT
RE-NU*
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MS-180"FREON"'TF DEGREASER— No need to disas-
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boards, motor parts. Eliminate grease, prevent re-
contamination. Non-conductive, non-flammable. Reduces
maintenance costs. MS-180 available in quarts, gallons,
and 5 gallons. " DuPont Trademark
MS-200 MAGNETIC TAPE HEAD CLEANER— Spray away
oxide dust before it ruins heads and tapes. MS-200
whisks It away. Manufacturers recommend it; communi-
cations experts prescribe it; EDP operators wouldn't be
without it. U.S. & FOREIGN PATS.
MS-230"CONTACT RE-NU"* — Renew your contacts.
"Contact Re-N u" does it. Knock out dirt, carbon, and other
contaminants. Will not harm insulation; leaves no residue.
Switch to MS-230 for your switches — and other points.
For FREE 16-oz. aerosol sample of any one of the above,
write (on your company letterhead, please), or use
coupon for free data.
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chemical co.,inc.
Danbury, Connecticut 06810 (203) 743-4447
□ Please send me data and prices on: SE
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INTENDED USE^
NAME
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STATE.
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CHICAGO • LOS ANGELES • TORONTO □ DIST. IN MILAN
HAMBURG • PARIS • LONDON • BEIRUT
Circle J 4 on Reader Service Card
www.americanradiohistorv.com
Picture Gallery-
45th AES Convention
Los Angeles' L. A. Hilton was host to the con-
vention held May 15 through May 18. As usual,
our camera lens was there and came away with
the pictures shown on these pages. If you want
detailed information on any of the products shown, circle
the appropriate number on the reader service card at the
rear of this issue. Material will be forthcoming directly
from the manufacturer or distributor.
'"11 mmcB 70 1,
'J5.4OO,(30
The broadcast market was not ignored
at AES. Langevin showed this clean
stereo console package. Circle 71
on Reader Service Card.
Haeco is noted for sophisticated
electronic designs. This is their lathe
control system. Circle 81 on Reader
Service Card.
It takes $35,400 to get thJs 20-16 console
with "View Scan" level indicators from
Audio Designs. Circle 59 on Reader
Service Card.
CO
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CD
CO
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<
■a
SCHOEPS
CONDENSER MICROPHONES
The Quality Standard
Throughout The World
A compatible microphone for all
powering systems
1 2V Centerfeed 12V Parallel
48V Centerfeed
Classical accoustic pattern shaping
;::«?» for uniform response
r,4* Exclusive single diaphragm
Hypercardiod pattern
World's smallest three pattern
condenser microphone
Utilizes standard American
scnm accessories
GATELY ELECTRONICS
57 WEST HILLCREST AVE. • HAVERTOWN, PA. 19083
. . . have you checked Gaiety (atefy? 215-446-1415
Circle 30 on Reader Service Card
As many as 26 in and 16 out on the
Son of 36 Grand by Auditronics also
had quad/stereo/mono mixdown.
Circle 94 on Reader Service Card.
Mark Levinson, a west coast distributor,
showed their own compact stereo
mixing board. Circle 49 on Reader
Service Card.
www.americanradiohistorv.com
Allison and API have cooperated in the
design of a mixing console computer
memol'y system. Circle 72 on Reader
Service Card.
Cetec is the new name, but Electrodyne
is the maker of this model 2000 board
with quad mixdown. Circle 70 on
Reader Service Card.
This demonstration board showed only
a part of the Waters fader line that is
available. Circle 60 on Reader Service
Card.
The English firm of Trident manufactures
consoles and components distributed
by Audlotechniques. Circle 82 on
Reader Service Card.
XT
Bushnell otters this compact console
for a variety of recording uses.
Circle 62 on Reader Service Card.
%0
Multiple woofers and wide dispersion
high end drivers are used in United
Sound Systems speakers. Circle 63 on
Reader Service Card.
James B. Lansing Sound showed
covered and uncovered versions of this
4350 model studio monitor. Circle 43
on Reader Service Card.
Among the studio monitor speaker line
of Altec's are these model 9846 and
9848 models. Circle 42 on Reader
Service Card.
Be sure
to attend . . .
THE AUDIO
ENGINEERING
SOCIETY'S
46th Technical
Meeting and
Exhibition of
Professional
Equipment
at the
Waldorf-Astoria
New York City
September 10-13
For details, write or phone.-
AUDIO ENGINEERING SOCIETY
BO E. 42nd St.. N Y.. N.Y
lOOlG • Phone: 861 8528 . . or
ftES PROGRAM INFORMATION
124 E. 40lh St.. N.Y.. N.Y.
lOOlG • Phone G61 2355
www.americanradiohistorv.com
Successor to the Crown DC-300 is the
improved 300 A. It has twice the output
devices. Circle 96 on Reader Service
Card.
Bose, long known for speaker systems
ins now into electronics with the 1800
800 watt stereo amplifier. Circle 90
on Reader Service Card.
Strom Communications makes a broard
line of amplifiers and speakers. This
is one of their huge horns. Circle 46
on Reader Service Card.
This demonstration of the Systron-
Donner tone generators and spectrum
analyzer was effective. Circle 93
on Reader Service Card.
BGW's massive power amplifier has 275
watts across 8 ohms, 550 across
4 ohms, 1500 across 1 ohm. Circle 85
on Reader Service Cards.
These components comprise the DuKane
line of equipment for audio spectrum
control. Circle 44 on Reader Service
Card.
CO
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00
We've qorOuRTliiNQToqEThER
DISC CUTTING EaulPMENT
• ORTOFON
ECHO DEVICES
• AKG • QUAD/EIGHT
KEPEX
• ALLISON RESEARCH
LIMITERS
• ALLISON RESEARCH
MICROPHONES
• ELECTRO-VOICE
AND WE'RE ON THE MOVE . . .
• SCHOEPS
MICROPHONE ACCESSORIES
• ATLAS • ELECTRO-VOICE
• SCHOEPS
MIXING EQUIPMENT
• PROKIT • GATELY SERIES 7 AND 8
. TASCAM
MONITOR LOUDSPEAKERS
• JBL • ELECTRO-VOICE
NOISE REDUCTION EQUIPMENT
• DOLBY
POWER AMPLIFIERS
• CROWN • PHASE LINEAR
RECORDING CONSOLES
• GATELY C1616 AND C2424 • TASCAM
TAPE DUPLICATORS
• AMPEX • PENTAGON
TAPE RECORDERS
• AMPEX • CROWN • METROTECH
• SCULLY • TASCAM
GATELY
ELECTRONICS, Inc.
In the EAST call
Bill Hamilton
215-446-1415
In the SOUTH call
Bill Brock
615-327-1746
57 WEST HILLCREST AVENUE • HAVERTOWN, PA. 19083
1907 DIVISION STREET • NASHVILLE, TENN. 37203
Circle 24 on Reader Service Card
www.americanracliohistorv.com
JOHN WORAM and LARRY ZIDE
db VISITS-Sound 80
ECENTLY, db packed its cameras and boarded a
Minneapolis-bound plane to pay a call on Sound
80, one of the midwest's most impressive con-
tributions to the world of recording studios.
Sound 80 began in 1969, when Herb Pilhofer, the music
director of the Minnesota Theatre Company, joined forces
with engineers Tom Jung, Scott Rivard and Gary Erickson.
In 1971, they moved into their present specially designed
building.
Sound 80 is a recording studio (five studios as a matter
of fact) with its own audio systems division and creative
services department. Old timers who still insist that all
recording sessions must be done within walking distance
of an ocean are advised to stay away from the twin cities
area.
Sound 80 boasts two 16 track studios, a quad mixdown
room, and 35 or 16mm film facilities. They've also in-
stalled a complete tape-to-disc transfer system. And in
downtown Minneapolis, on the 40th floor of the new I.D.S.
Center, they've just opened an elegant announcer studio
as a service to the local ad agency business. Since many
of the office buildings in this area are linked by pedestrian
passageways, the harried ad man need not even stop for
his coat when the inspiration for another brilliant recorded
announcement hits him.
All studios have their unique tales of construction prob-
lems and the I.D.S. installation is no exception. Located in
the next room is a psychiatrist's office. Now, although
many studios could really use a staff shrink on the prem-
ises, the analyst didn't think it would do much for his
patients' psyches if through the walls they heard the ad-
vantages of this or that detergent.
So, acoustical consultant Robert Hansen specified 500
square feet of lead shielding, weighing in at 7000 pounds,
for the wall separating the couch from the console.
Sound 80 Vice President and Chief Engineer Tom Jung
supervises the I.D.S. studio as well as the main studio com-
plex at 2709 East 25th Street. Also at this location is the
systems division, with design engineer Gary Erickson in
charge. Among other projects, the division designed the
Auto-Cue-2 system for the Stratford Theatre, (db, Decem-
ber, 1972).
And, the ZPE (Zero Position Error) Sync System is
also a product of the Systems Division. The device permits
two transports to be interlocked for 30 track recording
sessions or for video-audio work. Although not as complex
as other interlock systems, Sound 80 feels that its modest
price tag of about $2,000 may encourage smaller studios
to progress beyond 16 track with minimum expense. The
unit should be ready for marketing in the not-too-distant
future.
Creative Services is another facet of the complete Sound
80 concept. President and Director of Creative Services
Herb Pilhofer — who claims he would rather be on a
house boat on the St. Croix — may often be found in his
office working out an electronic music score on his ARP
and Moog synthesizers. Some time ago, Herb produced a
five (5?) channel presentation for Pan AM. He also
composed the musical score for the Guthrie presentation
of Julius Caesar as well as countless arrangements for
everything from commercials to classics.
Following, are photos taken at the Sound 80 studios.
Each has a self-explaining caption.
Sound 80's modern studio-headquarters building.
This capacious lobby greets the visitor to Sound 80 studios.
Tom Jung at the board and Herb Pilofer pondering during
a mixdown session.
Special effects for a t.v. commercial are created by
Herb Pilofer on one of the synthesizers at Sound 80.
www.americanradiohistorv.com
The view into ttie studio over the console. This picture The small announce studio in the I.D.S. building in downtown
was taken as Canadian producer Bob Burns recorded the Minneapolis. Engineer Bob Schultz assisted by Jacl^ie Maron
film score to Race Home to Die. A soundtrack album are at work recording a reading,
is scheduled for release on A & M records.
Two sixteen-track machines are interlocked during The ZPE "black" box. This synchroniser is expected to sell
a 30 track session. The ZPE syncronization system of in a commercial version for around $2000.
Sound 80's is used.
Record mastering is done on a computer controlled
Neumann lathe. Robert Berglund is in charge.
www.americanradiohistorv.com
W. A. RHEINFELDER
New Approaches to
Improved Tonal
Reproduction, Part 1
The author has spent at least fifteen years of experimentation
and research in audio circuit design aiming at better tonal
quality. This series is a product of that work.
WHEN SITTING DOWN to Hsten to a recording,
most of us are. annoyed to varying degrees
by imperfections of one sort or tlie other and,
depending on the degree of annoyance and
our technical slcill and knowledge, we do something or
little about it. When there is too much noise, we might
reach automatically for the treble control and turn down
the noise (and the treble content of the music) and arrive
at a different, not necessarily satisfying, condition which
might be more satisfying for the moment. The same kind
of action is often taken for excessive distortion, with similar
semi-satisfactory results; if the bass appears weak, we use
the conveniently provided bass control, and although it
may not accomplish what we were after musically, it does
change the sound character at the low frequencies, and
what else can be done anyway?
To a person with a keen ear, experiences like these are
exceedingly frustrating. If he becomes utterly distressed at
a harmonic distortion of 0.8 per cent, he obviously has a
harder time in achieving satisfactory reproduced sound
quality than the average listener, who will be quite happy
with ten to fifteen per cent distortion. Similarly, a musician
familiar with the tonal character of an instrument tends
to be less satisfied with reproduced sound than a person
who has never heard or played a live instrument.
The deficiencies common in a sound system are distor-
tion, (harmonic and intermodulation), noise (wide band
hiss and pop, extraneous tones, 60, 120 Hz and higher
harmonic hum, rumble, beats and interference, such as
the 15.75 kHz t.v. horizontal oscillator, the 9 kHz a.m.
station beat, etc.), and lastly, poor tonal balance, which is
a most common problem, but is tolerated amazingly well
by many people.
PROBLEMS WITH DISTORTION AND NOISE
It appears reasonable first to remove, as much as possible.
W. H. Rheinfelder is an engineering consultant, as well as
a musician.
the cause for the deficiency. For example, in the case of
distortion, the amplifier and speaker system should be
checked out, using measurement techniques and critical
listening tests. If the problem is not there, the source needs
to be worked on. With records, the stylus is often at fault,
and with a critical ear, it is easily found that unless both
angles of the stylus to the record surface are correct (and
in most practical cases they are not), the distortion will
be excessive even in an otherwise excellent system. As a
general rule, if you are distortion conscious and you have
a problem, it is most likely a stylus or tracking problem,
particularly if the system was good to begin with. Stylus
angles don't stay put! Other sources of distortion include
tracing distortion, pinch effect, tracking angle error, etc.
For the purist, stereo records produce less distortion if
they are played monophonically so that the high-distortion
vertical component is cancelled (which is often no loss
unless the stereo effect was pronounced and must be re-
tained at all costs). Theoretically, the difference between
channels A and B is less than the sum if they are equal
and in phase, which is practically not the case, and this
difference is recorded vertically in stereo records to achieve
less distortion because of the supposedly smaller amplitude,
while the sum is recorded horizontally as usual. Listening
to one channel only on stereo does not reduce the distor-
tion; it is necessary to use both cartridge outputs and phase
them to cancel the vertical component.
Removing the cause of a deficiency first is also practiced
with noise. Records can be kept clean, the stylus force can
be optimized, and hum can be removed. Thereafter, it
appears that the rest of the problems can be controlled by
the judicious use of filter, limiters, tone controls and equal-
izers; this approach has led to some truly astounding results.
THE PROBLEM WITH TONE CONTROLS
The problem of equalization and tonal balance had been
with the author for years until some rather drastic measures
were taken. It is easy to demonstrate the problem in listen-
ing tests. But it is difficult to correlate the effect one is
www.americanradiohistorv.com
ll\lo-
iM :
BASS
■ lOOK
— 1.002 p.
V\A^
lOK
lOOK
o OUT
; 200
IM
TREBLE
; 200
-20dB
I KHZ
20KHZ
'+20dB
-20dB
Figure 1. A loss-type tone control.
Figure 2. The typical response of the
circuit of Figure 1.
Figure 3. The circuit of a Baxendall
control.
hearing to frequency response measurements until one
goes to a very elaborate set-up described below.
A normal bass-treble control of the loss type is shown
in schematic form in Figure 1 and by action in Figure 2.
As can be seen, in boosting or cutting treble or bass, the
maximum action is achieved at the extremes in frequency
which is certainly undesirable. For example, for several
reasons which we shall discuss in more detail below, bass
frequencies of musical instruments are generally in the
region of 80 to 130 Hz. If we want to boost frequencies in
this region, for example by lOdB, we find that we are boost-
ing 20 Hz by 16 dB and we are boosting the whole region
below 80 Hz unduly. The same is true for the region
above 130 Hz, which causes a muddy juke-box type of
bass and all clarity is lost. Any boost in gain at frequencies
where there is no music can only increase extraneous
sounds, such as rumble, i/f noise, etc. Such a type of con-
trol has no musical value, although it is the most common
type of control in use. The high end function is not much
better and everybody knows how much music is lost and
how little is gained in noise improvement as the treble is
turned down.
An improvement was made years ago by a British engi-
neer named Baxendall.* This control uses feedback for tone
control (Figure 3) with two important results: reduction
in distortion and variable inflection points (Figure 4).
Inflection points are the points where the curve starts to
rise or fall. In Figure 2, all curves hinge around 1 kHz.
By contrast, in Figure 4, the hinge point wanders in from
the outside. It is possible to boost frequencies below 100
Hz, for example, while leaving frequencies above 100 Hz
unchanged. This cannot be done with the older type of
control. The Baxendall tone control is functionally much
better, costs no more, and is used in the better type of
equipment; however, it still leaves much to be desired. In
the maximum boost or loss position, it is identical to the
old style controls, and again it has maximum action at the
frequency extremes, where there is little or no music.
In the process of trying to find out what is the real cause
for such poorly balanced sound, the author tried the circuit
of Figure 5^ with rather pleasant results. The response of
the circuit of Figure 5 is compared with conventional bass
control in Figure 6. By some chance the bass boost
happened to be close to the actual musical bass frequencies
and the Q was about right. At this point it was decided
to develop a set of tone filters to expedite future research
and to really find out what was happening musically.
HIGH AND LOW PASS FILTERS
A survey of the literature showed quickly that it was easy
and relatively inexpensive to construct filters of 12, 18,
and 24 dB/octave slope. (The normal tone controls might
be called 6 dB/octave filters). In all these circuits feed-
back is used to sharpen the knee to make for a sharper
cut-off, instead of the round knee obtained by cascading
r-c sections. An 18 dB/octave filter requires three r-c
sections and a typical example is shown in Figure 7, which
is a high pass fiher with a cutoff below 20 Hz for the
values given. A typical filter of this type is shown in
Figure 8 with details in the references*'* ". Although these
filters have practical value, for experimental purposes a
somewhat sharper cutoff is desirable. Investigation dis-
closed a little known simple approach already given by
Williamson,^ which is capable of giving a slope in excess
of 40 dB/octave. The principle of these types of filters is
shown in Figures 9 to 12. Basically, a twin-T network is
used in conjunction with a feedback amplifier and a two
section r-c-network. Taking the output after the twin-T
produces a null and the extremely sharp cutoff (Figures
10 and 12). Taking the output before the twin-T (Figures
9, 11), results in a peak at the twin-T frequency which is
rolled off by the r-c sections and produces a very good dB/
octave filter. Based on the principle of Figures 10 and 12,
a high-low filter was constructed with the following logarith-
mically spaced cut-off frequencies: 22, 30, 40, 55, 75, 100
Hz and 4, 5.5, 7.5, 10, 13.5 and 18 kHz, all selectable by
rotary switches. By careful trimming, the peak before
cut-off was kept to about 0.3 dB and the second peak in
the cut-off region was 28 or more dB down. The circuit
for this combination filter is given in Figure 13. This
combination circuit is harder to trim because only one
feedback stage is used for both filters. Cascading of indi-
vidual high and low pass filters as shown in Figure 14,
allows somewhat easier design and accomplishes the same
purpose. Frequency response of these filters is shown in
Figures 15 and 16. Incidentally, in all practical filter cir-
cuits of this type, vacuum tubes or high voltage fets are
preferable to bipolar transistors. High input impedance
and low capacitance together with high gain, low noise,
and good output capability are very desirable. High voltage
Figure 4. Idealized response of the
Baxendall control of Figure 3.
20KHZ
20d8
-20dB
20dB
Figure 5. A special bass control
(reference 3).
.01
200K^ 'OOK
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IN
200 K 200 K
.02^
01
.05
Figure 6. A comparison of the circuit
of Figure 5 to normal bass boost.
-OOUT
20 HZ
+ 20dB
1 KHZ
www.americanradiohistorv.com
f = 20 HZ
Figure 7. A rumble filter with an 18 dB/octave rolloff.
Feedback produces a peak, rolled off by the r-c sections.
fets are reasonably priced and have all desirable features
such as 25 volts or more output at 0.1 per cent distortion,
less noise and better stability than bipolar transistors, to-
gether with input impedance and capacitance better than
the best vacuum tubes*"". One single fet of this type*
will do what would take many bipolars and much com-
plexity of circuit design. The only drawback is that the
bias resistor in the source must be individually determined
since manufacturers presently do not furnish values at the
eliminate individual frequencies to different amounts and
with different Q. Such a filter should be tunable from 20
to 20,000 Hz, permit a boost up to 30 dB, reject a fre-
quency to 60 dB. both with a variable Q from zero to 30.
At the same time, all other frequencies were to be constant
while the processing of the signal was taking place, with an
option of allowing the rejection of everything but the de-
sired tone. Such a filter was designed" and the schematic
is given in Figure 17 with the performance in Figure 18.
It is interesting to note that the requirement of 30 dB
boost and 60 dB rejection calls for a device in the bridge
section having a distortion of 90 dB down. A 12 BY7A
tube, of many devices tried, made the grade, when con-
nected as a triode and fine trimmed, and achieved a dis-
tortion of less than 0.003 per cent. In the practical con-
struction, replacement parts for a popular kit for a distor-
tion analyzer were used and balanced sufficiently well in
the Wien-bridge section. Work done with this unit dis-
closed the need for yet another piece of equipment for the
analysis of music.
MULTIPLE FREQUENCY EQUALIZER
For the ultimate in a tone control, it would be desirable
to be able to control many overlapping frequency bands
separately. Before coming up with a suitable circuit, much
+ B
Figure 8. A variable 18 db/ octave filter
(ret. 4)— 35 to 100 Hz and 5 kHz
to 14 kHz.
I2AX7
o — |L-^a/V-tH( — t-'WV
I IV I 270K
LOAD
470k
:^C2
O-VW
ISdB/OCT
Figure 9. A twin-T low pass peaking filter and response.
Figure 10. A twin-T low pass dipping filter and response.
l8dB/CCT
i -30dB
Figure 11. A twin-T high pass peaking filter and response.
Figure 12. A twin-T high pass dipping filter and response.
operating point. Finding the right bias resistor is a small
job, since maximum gain and least distortion coincide with
fets and the gain maximum is readily found.
A TUNABLE TONE FILTER
In addition to this cut-off filter, a very flexible tone filter
was designed. The idea was to be able to accentuate or
♦For example: T.I.2N5544, TIS79, TIS78. 2N5543; Teledyne 2N4883,
2N4886, etc.
research was done on selective feedback amplifiers. I had
once designed a graphic equalizer for use in motion picture
recording. While it was a good circuit for its purpose, it
used many iron-cored inductors which were not only ex-
pensive, but hard to tune and the Q was not easily con-
trolled. A simpler, more flexible feedback circuit was de-
sired and finally a bridged-T was used, together with a
phase shift network, to arrive at the desired response. The
final circuit is shown in Figure 19, together with the re-
www. americanradiohistorv.com
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3
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■o
CM
Figure 13. A combination hi-lo filter
based on Figures 10 and 12. Twin-t's
are shown at 4 kHz and 100 Hz.
Capacities in parenthesis must be
switched tor different cutoff frequencies.
Design points: 1. Twin-T null
frequency f 0=1.7 fc loss pass cutoff,
fo=fc/1.7 high pass cutoff; C1 and C2
tor maximum at 2 to and to/2
respectively; 3. C3, C9 for 0.2 dB rise
at 2 fo and fo/2 respectively; 4. R
is a fine adjustment for unity gain;
5. C6, C7 are optional for sharper
response.
flKC
+ 250
|T R 470K I
C7~ |470Kl
fc
fo
fo/2=fi
C
18 kHz
30.6 kHz
15.3 kHz
50 p
13.5
23.0
11.5
68
10.0
17.0
8.5
90
7.5
12.75
6.375
120
5.5
9.35
4.675
170
4.0
6.8
3.4
220
1. Select C2 tor max. gain at fo/2
2. Select CI tor + 0.3 dB at to/2
3. Select R1 tor 0 dB at to/10
(Includes source resistance)
Values given tor CI and C2 are
approximately .7.
Figure 14. A practical low pass filter.
sponses in Figure 20. This feedback circuit proved advan-
tageous for its low distortion and stability. Center frequen-
cies arrived at in the end were 40, 80, 160, 320, 640,
1280, 2560, 5120, and 10240 Hz. A similar piece of equip-
ment was available at one time commercially*, however,
with a totally different circuit. In the design of this unit
experimentation was carried out with different circuit Q's
which is readily done by changing a few resistors to alter
*Blonder-Tongue "Audio-Baton."
flTOK
-^AAr—
the feedback factor. With a Q=2, there was distinctive
ringing; in fact, it had to be judged worthless from a musi-
cal viewpoint. A Q=l proved ineffective to emphasize
musically important ranges and was also judged useless.
The circuit was then set in the middle at a Q of 1.41 and
listening tests showed very nice action. With a Q of 1.41 =
2, the frequency spacing must then be made on an octave
basis if the ranges are to overlap properly. It is wise to
l,t. tS.L S.*.M.t*.i.
SERIES 100 MIXERS
Series 100 mixers are available in the Model 16X4 prewired frame shown above
which accomodates up to 16 modules, and in the papular portable Model 8X4,
which takes up to eight modules.
The standard model 8X4-100-2C is a professional quality portable mixer meas-
uring 15x18x5" and weighing 18 lbs., has eight plug-in modules switchable to
200 ohm XLR-type mike inputs or line inputs, each providing push-button track
selection, echo send, equalizing, solo button, slider attenuators; two with
compressors. Integrated circuits throughout, four track outputs, max. 20 dbm
to 600 ohms with masters, VU meters, XLR output connectors, two monitor mix-
downs; other models with optional internal reverb. Price $2012.00 FOB
Houston.
Series 100 mixers may be had with any combination of seven modules:
Model lOOA standard equalizing Model lOOC compressor equalizing
Model lOOAP panpot equalizing Model lOOCP compressor/panpot
Model lOOAQ quad equalizing Model lOOCQ compressor/quad.
Model lOOB multifrequency equalizing
Other options include built-in reverb and the C-1 Cover for the 8X4. Call or
write for further details, prices, and address of nearest dealer. Dealer inquiries
invited.
INTERFACE ELECTRONICS
3SI0WESTHEIMER • HOUSTON, TEXAS 77027 • (713) 626-1'l90
0
-5
-10
-15
-20
S-25
-30
-35
-40
-45
fo = 2fi =l.70fc
RULb': FOR OPTIMUM RLSHWSEl
{.SELECT C2 FOR fi^AX. AT fi = fo/2
2. SELECT CI FOR +.3dB AT fi
3. SELECT Rl FOR OdB GAIN AT fi/IO
-3dB
•9^ Rl 300k
— ^Hww-w^
(120K)
»470k
(360):
;c2
20
50
100 500 IK
FREQUENCY IN HERTZ
Figure 15. Typical low pass response.
Figure 16. A high pass dip and rolloft filter.
+ 3dB
-.2dB
5K lOK 20K
fo
100 500 IK
FREQUENCY IN HERTZ
lOK 2GK
Circle 20 on Reader Service Card
www.americanradiohistorv.com
Figure 17. A filter with adjustable Q
from 0 to 30 and tunable 20-20,000 Hz.
Switch positions: 1. frequency elimina-
tion; 2. frequency peaking, gain at peak
changes with Q; 3. Frequency
peaking, gain at peak constant.
Note that d.c. filaments were used.
The resistors marked * used for fine
trimming. Resistor R may be used to
suppress skirts of response to equal
tuned circuit.
Figure 19. A selective tone equalizer.
Note that bias resistors in source
of fets are selected for maximum
gain In the range 1 to 10 kohms.
FOLLOWEB Q-CONTROL
GAIN STAGE
WIEN - BRIDGE
FOLLOWERS
put a frequency between the two hum frequencies of 60
and 120 Hz, not to unduly emphasize hum and harmonics.
The other frequencies are then automatically obtained.
With all this machinery, it was now possible to carry out
considerable music research, and some very interesting and
unexpected results were obtained. This research led to a
different, musician's type sound control, which will be
discussed next month.
ALL FETS TYPE
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www.americanradiohistorv.com
References
1. Chaffee, J. B. (Bell), U.S. Patent 2075503 (1936).
2. Baxandall, P. J., "Negative Feedback Tone Control,"
Wireless World, October, 1952, 402.
3. Rogers, G. L., "Simple RC Filter for Phonograph Am-
plifiers," Audio Engineering, June, 1947, 28.
4. Thiele, A. N. "Desing of Filters Using Only RC Sec-
tions and Gain Stages," Electrical Engineering, January,
1956, 31.
5. Thiele, A. N., "Variable Bandpass Filter," Radio-Elec-
tronics, June, 1956, 113.
6. Barber, B. T., "Desing of Continuously Variable Low-
pass Filter Utilizing Negative Feedback," Audio, March,
1954, 26.
7. Williamson, D. T. N., "High Quality Amplifier, New
Version," Wireless World, August, 1949, 282; October
1949, 365; November, 1949, 423.
8. Rheinfelder, W. A., "Fets Outperform Bipolars, Pen-
todes, in Voltage Amplifiers," Electronic Design, December
20, 1965.
9. Rheinfelder, W. A., "A Large Single Fet Amplifier?
Yes," Electronic Design, January 4, 1966.
10. Rheinfelder, W. A., "High Quality Microphone Am-
plifiers," Audio Engineering, June, 1947, 28.
11. Valley & Wallman, Vacuum Tube Amplifiers, (Mc-
Graw-Hill, 1946) Chapter 10, "Low Frequency Feedback
Amplifiers" _
versatile and compact
easy-to- use ,
consider the reverberating
things you can do.
RV~10
a small nxmiber for a
big system.
11929 Vosc Streein Norm Hollywood. Crtilorma 91605 □ 213/764-1516
Circle 26 on Reader Service Card
www.americanradiohistorv.com
DAVID A. HOWE
The Li'l Limiter
Figure 1. The schematic of the limiter
circuit tor audio signals at about
1 V nominal.
WHAT? Another design for a limiter? I suppose
each of us has dabbled in electronics deep
enough and long enough to realize that de-
signing a limiter is no easy task. The audio
man wants a box that will accept as much as +40 dBm
of signal dynamic range, will put out the input signal with
constant +0 dBm level, will not make the signal breathe,
grunt, or pop, has near zero distortion and noise, will work
with any signal from d.c. to light, and can be wired to limit
in a lot of ways (fast or slow attack and decay).
Big order, isn't it? Some fellows would be willing to pay
anything for this box. Well, this article will show you just
such a box. It'll cost you less than $15 plus a ± 10 V.d.c.
power supply. There's nothing critical about construction.
It can be built in one evening, but you'll probably play with
it for weeks.
Last summer I was doing consulting work for KBVL,
an f.m. radio station that wanted to go automated. I con-
cluded that the best investment for them was in a system
sold by Broadcast Products, Inc., a relatively new company.
When the equipment arrived, I was intrigued by the audio
mixer. It was a 24-channel mixer which was completely
voltage-controlled by another box, the computer. Each
channel was tied to the common programs bus through a
light-dependent resistor, or Idr. The Idr was in a small
sealed box with a 12-volt incandescent light bulb. Nothing
fancy, just a pilot light. Increasing the light intensity low-
ered the Idr's resistance. Full range of the Idr was roughly
100 k ohms to 20 ohms.
Here was a voltage-controlled attenuator with virtually
perfect signal transfer characteristics. The gears in my head
started turning. The Idr was a device around which one
could design mixers, oscillators, and equalizers, all voltage
dependent with wide dynamic range. The cost for the
Idr is a mere $3.86 from Broadcast Products, Inc. And
there's a second photo-resistive element added in the little
sealed container if you want to control two circuits at
a time.
David A. Howe operates Howe Audio Recording in Boul-
der, Colorado.
The schematic of the Idr limiter is shown in Figure 1.
The component types and values aren't critical. They were
picked for what I consider to be a limiter applicable to
most audio purposes.
Attack time is about 0.3 second. Release is about three
seconds. Increasing the value for Rl decreases the attack
time, and the release time can be changed by changing CI.
Rl multiplied by CI equals the time-constant of the feed-
back loop which is equivalent to the attack time. Since R4
divided by R3 is equal to one, the gain of the operational
amplified LM301 is unity. Any op amp you choose should
be wired for unity gain and should have all the extra com-
ponents needed to cause attenuation at frequencies much
higher than the natural resonant frequency of the loop.
Here it's roughly three hertz. By the way, if you make the
gain of the op amp greater than unity, the whole works
will go into oscillation, and you'll add a brisk vibrato on
a constant signal passing through the Idr.
The power supply should be able to furnish ± 10 V.d.c.
The +10 V supply has to drive the light in the Idr con-
tainer, so it should be able to deliver about 200 mA or
more. Just a few milliamps is all that's needed for the — 10
V supply.
There's nothing fancy about the resistive network where
the Idr is used. The input and output impedance of the net-
work will wander between 500 ohms and 1000 ohms as
the Idr changes resistance. For most of my applications,
this is tolerable since I usually derive a signal from a low
impedance emitter-follower and feed a relatively high im-
pedance load. In many applications, a constant input-output
impedance is necessary. I suggest a bridged-T network
such as the one shown in Figure 2. You'll need two Idr's
and another driver transistor. A bridged-T attenuator is
well suited because the bridge and shunt resistances change
linearly but in opposite directions.
Remember that the limiter uses a voltage-controlled
attenuator. Gain through the attenuator is always equal to
or less than unity. The amplifier feeding the limiter should
have a gain of two or more in order to put the limiter in
a working mode. In most cases, you can just increase the
amplification of a stage before the limiter. Usually ampli-
fiers have some amount of headroom. The purpose of a
limiter is to cut the amplitude down to size before going
www.americanradiohistorv.com
+ 10
tAAAtt
Figure 2. A voltage-controlled pad used in a bridged-T
configuration. Two Idr's are used.
to the input of another device. The peak level going through
the attenuator should be a volt or more.
My target was to come up with a limiter with excellent
specifications and a minimum number of parts. To change
this poor man's limiter into a rich man's, you can go for
a higher priced Idr. Some are sold with led's and come up
to full brilliance in less than a millisecond. Furthermore,
an led light source glows with intensities more linearly
proportional to the current flow through them. You may
like to build a single stage amplifier preceding the attenu-
ator since power supply voltages are available and you'll
probably have room for it. To make two or more limiters
track together as in the treatment of stereo signals, connect
each limiter's sample level lines together. You'll have to
balance each op amp using an external trimmer so that the
limiters are acting with similar amounts of attenuation.
You should refer to the op amp application sheet to deter-
mine where to add the trimmer.
My experience with the design of this limiter can be
simply stated: I was satisfied with it in every application.
And for the price, it's unbeatable.
HOW IT WORKS
With no audio signal applied through the Idr, the light
source is at full brilliance. There is very little attenuation
through the Idr and its resistive element will be less than
20 ohms. An audio signal passing through the Idr drives
emitter-follower Ql whose output is fed to an integrator,
Rl and CI. Attack time is fast by virtue of the low im-
pedance through Ql to +10 volts; release time is slower
through the 100 k resistor to — 10. The d.c. level out of
the integrator (sample level) will roughly equal the peak
voltage of the audio signal passing through the Idr.
Differential amplifier LM301 compares the sample level
with a reference level. The reference may be manually ad-
justed or can be derived from any external source. The
amplifier has unity gain. A difference voltage between the
sample and reference shows up at the base of Q2. Since
Q2 drives the light in the Idr, a change in the light's bril-
liance will occur which tries to correct the error; that is,
the difference between the sample and reference. Rl and
CI determine the time-constant for the loop, or how fast
the loop responds. Rl can range from just a few ohms to
as high as several hundred thousand ohms. R3 and R4
determine the loop gain. A gain of near unity carries the
risk of having the limiter act too "violently." Program
material will be "hard-limited" and loud excursions may
cause overshoot. However, this circuit contains enough
losses in the loop, such as through Ql and the integrator,
that the total gain is less than unity by a comfortable
amount. Increasing R3 will lower the feedback loop's gain
still further, making the limiting "softer." ■
Professional Quality
(AT AN UNPROFESSIONAL PRICE)
What do professional sound contractors and the lead-
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Phase Linear amplifiers?
POWER: Good sound systems need ample power.
The Pliase Linear 400 amplifier provides more than
200 Watts per channel of distortion-free music at a
price of about half of any competing amplifier based
on a dollar/watt basis.
AVOIDS CLIPPING: Most good amplifiers suffer
from clipping and generate high distortion during low
frequency passages and on musical peaks. Enough
power is supplied by the '400' to greatly reduce this
problem.
RELIABILITY: Our '400' is checked and rechecked
to insure lasting reliability. Phase Linear takes pride
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SPECIFICATIONS
POWER: Greater than 200 watts/channel R.M.S., both channels
driven into eight ohms, 5 to 20 kHz.
POWER AT CLIPPING: Typically 250 watts/channel R.M.S. into
8 ohms, 400 watts/channel R.M.S. , into 4 ohms, 125 watts/channel
R.M.S. , into 16 ohms.
HARMONIC OR I.M. DISTORTION: Less than .25%. Distortion
is typically less than .05%.
DAMPING RATIO: Greater than 1 ,000: 1 @ 20 Hz.
PROTECTION: Electronic energy limiters together with supply
fuses prevent excursions into the unsafe operating' regions.
Whether you need power for a sound system or a 'State of
the Art' home stereo system, the Phase Linear 400 can
make your speakers come alive. Join the professionals - use
TOMORROW'S AMPLIFIER - TODAY!
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Don Davis. Provides solid understanding
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24. Basic Electronic Instrument Handbook.
Edited by Clyde F. Coombs, Jr. Hewlett-
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for all instruments. Offers saving in time
and effort by having complete Information
in one volume on how to get the most bene-
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pages. Hardbound. $28.50
25. Operational Amplifiers-Design and
Applications. Burr-Brown Research Corp.
A comprehensive new work devoted en-
tirely to every aspect of selection, use, and
design of op amps— from basic theory to
specific applications. Circuit design tech-
niques including i.e. op amps. Applica-
tions cover linear and non-linear circuits,
A/D conversion techniques, active filters,
signal generation, modulation and de-
modulation. Complete test circuits and
methods. 474 pages. $15.00
26. The Design of Digital Systems. John
B. Peatman. Textbook for students desiring
to develop a creative approach design capa-
bility through digital systems approach.
Answers these question: Under what cir-
cumstances it is desirable to implement a
system digitally? What are some of the
components available for implementing
the system? How do we go about design-
ing it? 448 pages. $15.50
31. Solid-State Electronics. Hibberd. A
Basic Course for Engineers and Techni-
cians. An extremely practical reference
book for anyone who wants to acquire a
good but general understanding of semi-
conductor principles. Features questions
and answers, problems to solve. 1968.
169 pp. $9.95
32. Circuit Design for Audio, AM/FM, and
TV. Texas Instruments. Texas Instruments
Electronics Series. Discusses the latest ad-
vances In design and application which
represent the results of several years re-
search and development by Tl communica-
tions applications engineers. Emphasizes
time- and cost-saving procedures. 1967.
352 pp. $14.50
35. An Alphabetical Guide to Motion
Picture, Television, and Videotape Produc-
tions. Levitan. This all-inclusive, authorita-
tive, and profusely illustrated encyclopedia
is a practical source of Information about
techniques of all kinds used for making and
processing film and TV presentations.
Gives full technical information on mate-
rials and equipment, processes and tech-
niques, lighting, color balance, special
effects, animation procedures, lenses and
filters, high-speed photography, etc: 1970.
480 pp. $24.50
40. Radio Transmitters. Gray and Graham.
Provides, in a logical, easy-to-understand
manner, a working knowledge of radio
transmitters for quick solution of problems
In operation and maintenance. 1961. 462
pp. $16.00
23. Wide Screen Cinema & Stereophonic
Sound. M.Z. Wystozky. First published In
USSR In 1965 this excellent English trans-
lation covers wide gauge films, panoramic
films, circular panoramic cinematography;
technical fundamentals of stero sound re-
cording for film, as well as details of the
Soviet systems now in use. 284 pages.
$15.00
33. Noise Reduction. Beranek. Designed
for the engineer with no special training
in acoustics, this practical text on noise
control treats the nature of sound and its
measurement, fundamentals of noise con-
trol, criteria, and case histories. Covers
advanced topics in the field. 1960. 752 pp.
$19.50
16. Magnetic Recording. Charles E. Low-
man. Reference guide to the technology
of magnetic recorders used in audio re-
cording, broadcast and closed-circuit TV,
instrument recording, and computer data
systems. Includes latest information on
cassette and cartridge recorders; TV re-
corders; direct and FM signal electronics
from low to wideband; servo-control and
signal record /playback circuitry; cap-
stan, reel, and head-drum servos for
longitudinal, rotary, helical-scan, and
disc recorders. Glossary, index, biblio-
graphical information. 274. pp. $14.50
28. Environmental Acoustics. Leslie L.
Doelle. Applied acoustics for those in envi-
ronmental noise control who lack spe-
cialized acoustical training. Basic informa-
tion in comprehensible and practical form
for solving straightforward problems. Ex-
plains fundamental concepts; pure theory
minimized. Practical applications stressed,
acoustical properties of materials and con-
struction listed, actual installations with
photos and drawings. Appendixes illustrate
details of 53 wall types and 32 floor plans
and other useful data. 246 pgs. $18.50
13. Acoustic Design & Noise Control.
Michael Rettinger. 1973. NEW, revised
and enlarged edition covers physics of
sound, room acoustics and design, noise
and noise reduction, plus noise and its
problems. Many charts and graphs. A
practical and useful book. 562
pages. $22.50
22. Acoustics of Studios and Auditoria.
V.S. Mankovsky. Basic theory plus a mass
of design data covers the field with special
reference to studios and places of public
performance. For acoustical designers and
specialists in sound transmission in cinema
and broadcasting. Features exhaustive
treatment of studio acoustics by the sta-
tistical, geometric and wave methods in
parallel. 416 pgs. $15.00
a.
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Send copy to: Classified Ad Dept.
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FOR SALE
THE ABSOLUTE SOUND, a reader-sup-
ported quarterly about audio and music,
has reviewed in its first two issues: the
Dayton-Wright full-range electrostatic;
the l^agneplanar; the Hegeman l^odel
One; SME's low-mass arm; the Crown
DC-300A (among other things). Coming
up: Three new cartridges from Japan,
the Grace, Satin and Supex; the II^F
lyionitor III; Panasonic SP-10 turntable;
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techno-freaks: the reviews are rigorously
subjective.) Cost: $8.00 annually (four
issues). THE ABSOLUTE SOUND, Box
115x, Sea ClifT, N.Y. 11579.
PRE-EQUALIZED J.B.L. & ALTEC IWONI-
TORS; D.B.X. Companders; Little Dip-
per hum/buzz notch filters; Cooper Time
Cube echo delay; B.B.C. & \.M.F. refer-
ence monitors; Lamb "B" Dolby pro-
cessors; Ortofon and B & O ultra-track
cartridges; Schoeps & A.K.G. condens-
ers; Beyer ribbons; U.R.E.I. comp/limit-
ers; Gately pro-kits; Infinity electrostat-
ics; Crown amplifiers/ recorders; Tascam,
Community Light & Sound fiberglass
horns; Q.R.K.; dozens more. Shipped
prepaid/insured from Music & Sound,
Ltd., 11-1/2 Old York Rd., Willow
Grove, Pa. 19090. (215) 659-9251.
10.5" RECORDER SPECIALISTS. Wanted:
used metal 10.5" reels and flanges for
Va" tape in good condition; $.75 each
with box; subtract $.15 for no box; oc-
casionally buy salvage reels and tape;
write giving condition. P.O. Box 338,
Dunwoody, Georgia 30338.
FOR SALE: AUTOMATED PROCESSES
model 2061 console, 2 years old; 16-in/
8-out; $18,500. For detailed information,
call (901) 388-1032.
TEKTRONIC OSCILLOSCOPE, 535A with
dual trace, triggered and delayed sweep.
$585 or best offer. G. Daly, 33 Walnut,
Mill Valley, California 94109. (415)
383-6642.
TASCAM MIXING CONSOLES— $1,890.
Tascam Vi-inch recorders — $1,770.
Shipped prepaid/Insured including free
alignment and calibration. Music &
Sound, Ltd., llVi Old York Rd., Willow
Grove, Pa. 19090. (215) 659-9251.
SPLICE FASTER, BETTER BY SHEAR-
ING . . . replaces razor; specify .250-
inch or cassette: $16.95. With attached
splicing tape mechanism, $24.95. Details-
NRP Box 289, McLean, Va. 22101.
www.americanradiohistorv.com
CATV— MATY PRODUCTS
• CONNECTORS • WAIIPIATES
• SPLITTERS • AMPLIFIERS
^^^^^
AVA ELeCTRONlCS CORP-
iQNc LAME vmu OAit»v, PA \mi
STUDIO TAPE ELECTRONICS. Advanced
design Incorporates all the desired fea-
tures for updating or expanding out-
dated recorders or building new sys-
tems. Prompt delivery. InovonieS, Inc.,
1630 Dell Avenue, Campbell, Co.
95008.
BROADCAST AND RECORDING EQUIP-
MENT: Scully; Metrotech; Langevlne;
Electrodyne; Q.R.K.; Micro-Trak; M.R.L.;
Nortronlcs; McMartin; U.R.E.I.; Neu-
mann; E.V.; A.K.G.; Sennheiser; Tascam;
Atlas; Ferrograph; HAECO; Stevenson;
Gately; D.B.X.; Advent; Altec; Fairchild;
Audio Designs; 3 M; Magnacord; Telex;
Inovonics; disc recording systems; pack-
age deals; installations; service. Wle-
gand Audio, Middleburg, Pennsylvania
17842. (717) 837-1444.
AMPEX, SCULLY, TASCAM; all major
professional audio lines. Service, expe-
rience, integrity. 15 minutes George
Washington Bridge. Professional Audio
Video Corporation, 342 Main St., Pat-
erson, N.J. 07505. (201) 523-3333.
CROWN TAPE RECORDERS, amps; IMF
monitor speakers; AKG professional
microphones; UREI limiting. Little Dip-
per; Fairchild; Crown warranty service
station, more. Barclay, 503 Haverford
Avenue, Narberth, Pa. 19072. (215)
667-3048. or 120 Villa Crest Dr., State
College, Pa. 16801. (814) 238-1598.
HAECO announces complete repair ser-
vice and overhaul for all Westrex cut-
terheads. Conversions of 3D-II and old-
er models to higher performance stand-
ards and reliability. IHelium cooling
systems and hi-temp coils can protect
your investment. Repair insurance pro-
gram available. Rapid service. Lower
cost. HAECO, 14110 Aetna, Van Nuys,
California 91401.
LOWEST PRICES for stereo masters ex-
pertly cut on a Scully lathe with the
Westrex 3D stereo cutting system.
Stereo: 12-inch — $33 per side; 7-inch —
$14 per side. Mono: 12-inch— $22 per
side; 7-inch — $9 per side. We also cut
demos — prices even lower. Trutone Rec-
ords, 6411 Bergen wood Ave., North
Bergen, N.J. (201) 868-9332.
ONE STOP FOR ALL your professional
audio requirements. Bottom line ori-
ented. F.T.C. Brewer Company, P.O.
Box 8057, Pensacola, Florida 32505.
CROWN CX 822, used. Barcloy (dealer)
503 Haverford Ave., Narberth, Pa.
19072. (215) 667-3048.
PRE-EQUALIZED J.B.L. MONITORS; Lit-
tle Dipper hum/buzz notch filters;
Cooper Time Cube echo-send-delay;
B.B.C. reference monitors; Lamb "B"
Dolby processors; Ortofon ultra-track
cartridges; Schoeps/A.K.G. condensers;
Buyer ribbons; U.R.E.1. comp/limiters;
Gately pro-kits; Infinity electrostatics;
Crown amplifiers/ recorders; dozens
more, plus class (A) warranty service
station. Shipped prepaid/insured from
Music & Sound Ltd., I1 1/2 Old York Rd.,
Willoy^ Grove, Pa. 19090. (215) 659-
9251.
TWO-CHANNEL MONITOR EQUALIZERS
for your Altec's and J.B.L's are a steal
at $150. Music & Sound, Ltd., \V/i Old
York Rd., Willow Grove, Pa. 19090.
(215) 659-9251.
SOLID-STATE AUDIO MODULES. Con-
sole kits, power amplifier kits, power
supplies. Octal plug-ins — mic. eq. line,
disc, tape play, tape record, amplifiers.
Audio and tape bias oscillators. Over 50
audio products, send for free catalog
and applications. Opamp labs. Inc., 172
So. Alta Vista Blvd., Los Angeles, Ca.
90036. (213) 934-3566.
NEW YORK'S LEADING supplier of pro-
fessional audio/video equipment and hi-fi
stereo components. All major brands in
stock. Call for quote — sales — service —
leasing — trade-ins Martin Audio, 320
West 46th Street, Nevtr York, N.Y.
10036. Telephone: (212) 265-6470.
AMERICA'S LARGEST SELECTION of
new and used broadcast and recording
equipment! Latest bulletins available.
The Maze Corporation, P.O. Box 6636,
Birmingham, Ala. 35210.
WHATEVER YOUR EQUIPMENT NEEDS
— new or used — check us first. Trade
your used equipment for new. Write for
our complete listings. Broadcast Equip-
ment & Supply Co., Box 3141, Bristol,
Tenn. 37620.
AUDIO EQUIPMENT, new and used; cus-
tom consoles built to your specifications
using the components of your choice.
Whether you're building a new studio
or remodeling your present one, check
us first for a package price. Amboy
Audio Associates, 236 Walnut St., South
Amboy, N.J. 08879. (201) 721-5121.
WANTED
BACK ISSUES WANTED. Dates? Price?
Condition? Cone, 775 South Madison,
Pasadena, California 91106.
EMPLOYMENT
WANTED: EXPERIENCED SENIOR EN-
GINEER with solid following or small
broad-based studio/ production house to
join forces with growing top quality
studio. Contact Jerry Kornbluth, A & J
Audio/Visual Services, Inc., 119 W.
57th St., New York, N.Y. 10019. (212)
247-4860..
WANTED: RECORDING ENGINEER
$12,000 - $18,000/Yr. Negotiable
"Do you have a total knowledge
of all aspects of audio recordings?
"Can you appreciate all forms of
rock and soul and get along with
all types of personalities?
'Can you take raw musical talent
and convert it into a sellable prod-
uct on tape?
*Do you know the sound of a hit?
Do you want to cut hits? Do you
want success badly enough to eat
every top selling single and LP
you're not on?
*ln short, are you a born winner?
If you can honestly answer "yes"
to all the above, we want you to
join us and we'll pay whatever's
fair. Track Recorders has had eight
national chart records in the last
year. Washington, D.C. is the last
major music frontier and we're the
leaders. Our studio has all the
standard quality equipment — 3M
16-track, 25-in/16-out custom con-
sole, EMT reverb, JBL 4320 moni-
tors, Dolby, Kepex, varispeed, grand
piano, Hammond B3 organ, amps,
drums, excellent test gear and
maintenance. Your weekends will
generally be free. The Washington
area offers great entertainment plus
Blue Ridge Mountains, Shenandoah
Valley, Chesapeake Bay, Atlantic
Ocean.
Call or write to: TRACK RECORDS,
INC., 8226 Georgia Ave. #11-2,
Silver Spring, Md. 20910. (301)
589-4349.
pliii^i T O * 1°^ 1/
8 and 16
TRACK RECORDING CONSOLES
THE SOUNDEST DOLLAR SPENT
IN PRO AUDIO TODAY
1965 CHEREMOYA AVE.,
HOLLYWOOD, CALIF. 90028
P.O. Box 3187, Hollywood, CA. 90028
(213) 467-7890
www.americanradiohistorv.com
PEOPLE, PLACES, HAPPENINGS
• Arthur A. Shubert, Jr. has been
appointed chief development engineer
for Neve Electronic Laboratories, Ltd.,
Melbourn, England. Mr. Schubert, who
was formerly chief engineer for Rupert
Neve, Inc. in Connecticut, will be re-
sponsible for the development of new
techniques and new products for the
Neve line of professional sound con-
trol consoles. Another Neve appoint-
ment is that of Barry J. Roche, who
joins Rupert Neve, Inc. in the senior
engineering position. Mr. Roche was
formerly manager of technical services
and responsible for post-installation
customer liaison for Neve in Great
Britain and Europe.
The Second Annual Nashville Re-
cording Arts Seminar rakes place
August 22nd through the 26th. The
place is the Sheraton Motor Inn, 920
Broadway, Nashville, Tennessee. The
purpose of the seminar is to help
everybody share new and old ideas
and learn more about the recording
industry. Sponsors of the seminar are
Nashville Record Productions and
Fanta Sound. Cost for the programs
is $35, not including motel and food.
Some of the important topics to be
covered include Ins and Outs of Moni-
tor Speakers, A to Z on Equalization,
Financing the Studio, Power Ampli-
fiers, Use of Test Equipment, and
Basic Acoustics. There will be speeches
and demonstrations by a number of
manufacturers, question and answer
sessions with some of the top mixers
in Nashville, and there will be a Flea
Market permitting the sale (or pur-
chase) of items brought by participants.
Call Johnny Rosen at Fanta Sound
for further information. He can be
reached at (615) 327-3768.
• Quad/Eight Electronics has formed
a new sales subsidiary to service over-
seas customers,, including Canada and
Mexico. The new division, known as
Quad/Eight International, will be lo-
cated at the parent company in North
Hollywood, California under the direc-
tion of Quad/Eight marketing director,
Ron Neilson.
• A new studio, offering 8- and 16-
track recording, has been opened by
Clear Light Studios, in Bayside, Queens,
N.Y. The new studio is equipped with
the latest MCI mixing console, Scully
and Ampex tape decks, dbx noise re-
duction, and auxiliary equipment. Oper-
ated by Louis Duka and Joel Schwartz,
Clear Light has, for the past two
years, cut demos for some prominent
performers, including Miles Davis,
Benny Goodman, and Aretha Frank-
lin.
• A book on guiding those interested
in audio engineering as a career is
bing prepared by Paul S. Moverman.
The author has requested that those
institutions dealing with education in
the audio industry send him full in-
formation regarding the courses they
offer. The book will attempt to explore
all courses in the audio engineering
field, covering the syllabus of each
course and the credentials of the in-
structors. U.S., Canadian, and Euro-
pean schools will be included. Please
send information to Mr. Moverman,
c/o db, 980 Old Country Rd., Plain-
view, N.Y., 11803.
• Daniel E. Denham has been ap-
pointed vice-president of the newly
formed recording materials group of
the 3M Company. Denham's new
group, the result of a reorganization of
the magnetic products aspect of the
firm's business, will comprise the mag-
netic audio video products, data re-
cording products, Mincom, and film
and allied products divisions. Other ap-
pointments effectuated by the reorgan-
ization include Dr. M. R. Hatfleld, a
chemist, named vice president of the
Mincom division, Robert Herr as vice
president of the data recording prod-
ucts division, and John E. Povolny,
named general manager of the mag-
netic audio products division. William
A. Aitken continues as general man-
ager of the film and allied products
division.
• Altec Corporation, of Anaheim,
California, has announced the forma-
tion of a subsidiary corporation, Altec
International (U.K.) Ltd., at Steven-
age, Hertfordshire, England, to de-
velop the European market for prod-
ucts manufactured by its Sound Prod-
ucts Division. The new branch will be
headed by J. P. (Ben) Hogan.
IMPORTANT
ANNOUNCEMENT TO
MANUFACTURERS OF
PROFESSIONAL AUDIO
EQUIPMENT
Sagamore Publishing Co., Inc.
publishers of db — is planning
to publish a Directory of Pro-
fessional Audio Products. A
questionnaire requesting com-
pany and product information
has been sent to all manufac-
turers asking that they respond
by the deadline indicated to
assure their free listing in this
important directory.
If for any reason you are a
manufacturer of professional
audio equipment and have not
received your questionnaire,
or have misplaced or misfiled
your copy, please write imme-
diately for another copy. Com-
plete instructions are included
for your listing.
If you wish any further details
please write Larry Zide, editor,
at Sagamore Publishing Co.
Inc., 980 Old Country Rd.,
Plainview, N.Y. 11803. Infor-
mation concerning advertising
may be obtained from H. Krantz
at the same address. Phone
(516) 433-6530.
www.americanradiohistorv.com
TheOuietOne...
Time was when hand-held microphones could mean a handful of problems.
Now, the Shure SM61 professional omnidirectional dynamic microphone
combines sleek good looks with extraordinary reduction in cable and han-
dling noises. The SM61 is built around a shock mount that effectively reduces
cable, tiandling and mectianical noises to insignificant levels. A super-
efficient "Blast Barrier" cuts wind and breath noise to a negligible minimum.
Smooth, wide-range response produces an extremely natural, coloration-
free sound that does great things for speech, vocal music and instrumental
pickup. The SM61 is beautiful to look at, a delight to work, a pleasure to
hear. Write for a complete data sheet to:
Shure Brothers Inc.
222 Hartrey Ave., Evanston, III. 60204
In Canada: A. C. Simmonds & Sons Ltd.
Circle 1 1 on Reader Service Card
www.americanradiohistorv.com
Please don't dance
on your tape recorder!
We've seriously gone about the
business of designing tlie best possible
loudspeaker for monitor use. With
computers, and anechoic chambers,
and all the rest. And, having gained
a monster new insight into bass speak-
er performance, we've come up with
what looks like a winner. The
Sentry III.
We've run all the curves that prove,
in a most scientific, sober fashion,
that the system is really quite good.
We've got polar graphs, and frequency
response curves, distortion measure-
ments, total power output curves,
power handling test results, and SPL
data galore.
-
But what happens when we dem-
onstrate the Sentry III? Leading
engineers (whose names we hesitate
to divulge — but you know them) leap
about in their control rooms DANCING
for heaven's sake! Snapping their
fingers and feeling the sound, and
reveling in the sensory pleasure of a
clean first octave. And last octave too.
for that matter.
And they run from one side of the
studio to the other trying to find holes
in the distribution of the highs . . .
and they can't ... and they LAUGH!
It's very unseemly {but secretly quite
gratifying). So we try to thrust our
good numbers and graphs at these
serious engineers, but they'd rather
listen and compare and switch speak-
ers. And make rude remarks about their
old monitors.
Who will stand still long enough to
heed our technical story? Perhaps
you're the serious-minded, sober-
sided engineer we're looking for. If so,
by all means write us. We've got quite
a stack of strait-laced, objective
literature describing the new Sentry III
monitor loudspeaker just waiting to
be seen and appreciated.
And after you've read our story,
perhaps we can arrange a demonstra-
tion of this new speaker for you. The
Sentry III. Bring your tap shoes.
New SENTRY III
Monitor Loudspeaker
Gullon
COMPANY
SENTRV III Freqjency Response 40 18.000 Hz ± 3 OB; Sojnd Pressure on Ajis at 4' wild 50 wall input 113 dB: Disoersior 120° horizontal. 60° vertical;
Size 2»y,\N X ioyiO X 2i'/iH; Weight I661bs. $600.00 suggested prolsssional ret. SEO active equalizer extends response to 28 Hz, S60.00.
Circle 12 on Reader Service Card
ELECTRO-VOICE, INC., Dept.831BD, 686 Cecil St., Buchanan, Michigan 49107
www.americanradiohistorv.com
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